The invention concerns a folding tray of the type formed by a single foldable blank, the blank comprising a bottom wall, foldable lateral walls, and foldable corner elements situated between adjacent lateral walls. Each corner element includes triangular folding parts joined to each other by a fold line. The lateral walls and corner elements carry foldable border sections which define a horizontal rim along the outer periphery of the erected tray.
Folding trays of this general type, which may be closed tightly by means of a cover set onto the border flange, are used, for example, for the packaging of meats or ready made meals. The trays are known to have problems in their corner zones, however. Most of the known folding trays comprise at each corner, several triangular folding parts, the apexes of which are located at the intersection of the bottom and the side walls (e.g, see the triangular parts 17, 18 of German Patent No. 28 19 708). These folding trays cannot be closed in a gas-tight manner in actual practice, as the border sections associated with the triangular folding parts must always be cut very deeply in order to make possible their folding at all. In actual practice, this cut can never be covered completely. If, on the other hand, the cut is eliminated, the paper is stretched by the folding angle to the extent that the border flange is torn.
To remedy this situation, substantially rectangular center pieces have been interposed between the triangular folding parts (e.g., see rectangular parts 10 in German Patent No. 21 33 297) so that the folding angle is reduced in the corner areas, thereby reducing the stretching of the material and diminishing the risk of tearing. In the case of these folding trays, it is often not necessary to apply cuts to the border flange. However, due to the fact that such folding trays form a circular arc at the border flange, the rectangular centerpiece is caused to curve, which, in turn, leads to a slight bulging of the border flange from its flat position. A satisfactory tight sealing of the folding tray is therefore made difficult.
It is an object of the invention to provide a folding tray of the afore-mentioned type, whereby gas-tight sealing is made possible or is facilitated by keeping the peripheral border flange flat.